The present invention relates to a guide wire, particularly to a guide wire for use in introducing a catheter into a body lumen such as a blood vessel, and to a method of manufacturing the same.
Guide wires are used to guide a catheter in treatment of cites at which open surgeries are difficult or which require low invasion to the body, for example, PTCA (Percutaneous Transluminal Coronary Angioplasty), or in diagnosis such as cardioangiography, and for the like purposes.
A guide wire used in the PTCA procedure is inserted, with its distal end projecting from the distal end of a balloon catheter, into the vicinity of a target angiostenosis portion together with the balloon catheter, and is thus used to guide the distal end portion of the balloon catheter to the vicinity of the target angiostenosis portion.
Particularly, a guide wire used to insert a balloon catheter into a blood vessel is required to go forward in a complicatedly meandering blood vessel, and is therefore required to have sufficient flexibility and restoring performance against bending, pushability and torque transmission performance (these are altogether called operationality) for securely transmitting an operational force from the proximal end portion to the distal end side, kink resistance, and the like. As this kind of guide wire used for a catheter, there have been proposed a guide wire in which a coil having flexibility against bending is disposed around a small-diameter core member for providing the distal end portion with appropriate flexibility, and a guide wire comprising a core member formed of a superelastic material such as a Ni—Ti alloy for attaining flexibility and restoring performance.
In the conventional guide wires, the core member is substantially made of a single material. Therefore, the flexibility of the distal end portion of the guide wire is lost where a material having a comparatively high elastic modulus is used for forming the core member in order to enhance the operationality of the guide wire. On the other hand, if a material having a comparatively low elastic modulus is used for the core member in order to obtain flexibility at the distal end portion of the guide wire, the operationality on the proximal end side of the guide wire is lost. Thus, it has been regarded as difficult to satisfy both the requirements of flexibility and operationality by using a core member made of a single material.
For solving the above problem, there has been proposed a guide wire in which a Ni—Ti alloy wire is used as a core member, and the distal end side and the proximal end side of the alloy wire are heat-treated under different conditions in order to enhance the flexibility of the distal end portion of the alloy wire and to enhance the rigidity on the proximal end side of the alloy wire (U.S. Pat. No. 5,171,383). However, such a control of flexibility by heat treatments has a limitation; for example, even if a sufficient flexibility is obtained at the distal end portion of the alloy wire, a satisfactory rigidity may not necessarily be obtained on the proximal end side of the alloy wire.
Also, there has been proposed a guide wire which is comprised of a flexible wire disposed on the distal end side, a high-rigidity wire disposed on the proximal end side, and a tubular joint member connecting the first wire and the second wire and being provided with a groove and a slit, wherein the rigidity of the joint member increases gradually from the distal end side toward the proximal end side (U.S. Pat. No. 6,001,068). This guide wire shows a sufficient effect. However, there is still a demand for a guide wire in which the variation in physical property is more gradual, the torque transmitting force and pushing force can be transmitted from the proximal end portion to the distal end side more securely, and the distal end portion is more flexible.
The present invention has been made in consideration of the above-mentioned problems in the prior art.
It is an object of the present invention to provide a guide wire having a sufficiently flexible distal end portion and further enhanced in torque transmission performance and pushability, and a method of manufacturing the same.